The invention relates to an automatic embroidery sewing machine, and in particular, to such machine which is provided with an embroidery frame drive mechanism including a plurality of servo motors and also provided with an electronic control system which automatically controls the operation of the drive mechanism in synchronism with the elevating motion of a needle of the machine.
In an embroidery sewing machine including a pair of servo motors which are controlled to produce respective drive outputs in accordance with a storage of strokes of an embroidery frame for each stitch so as to represent components of the motion along two coordinates and in which the outputs are combined to provide a composite motion of the embroidery frame tracing a desired two-dimensional figure in synchronism with an elevating motion of a needle of the machine, the maximum stroke imparted to the embroidery frame for each stitch is limited, for each coordinate component, to the order of 4 mm, for example, since it is not advisable to provide an unduly high capacity of the servo motors. Consequently, a plurality of stitches must be continued one after another for a stroke which exceeds the maximum value. After one embroidery operation is completed, the sewing yarn which extends along the loose courses between parts of a pattern must be removed. The removal is a troublesome operation where an increased number of stitches are involved.
Where the capacity of the servo motors is increased to provide a maximum stroke along each coordinate of 10 mm or greater for each stitch, the length of time required to complete a desired embroidery pattern can advantageously be reduced. However, the proportion of a cloth feed which requires an increased stroke on the order of 10 mm per stitch represents about 10% of all the stitches required for the entire pattern. It will be seen that the provision of servo motors of an increased capacity for such less frequent purposes and a corresponding increase which is required in the output capacity of an associated control circuit are not an efficient way of solution. Hence, it is desirable that an increased maximum stroke for each stitch be provided without requiring an increased size or capacity and an increased speed of operation of an embroidery frame drive system.
It is a first object of the invention to provide an automatic embroidery sewing machine allowing an increased maximum stroke per stitch.
It is a second object of the invention to provide an automatic embroidery sewing machine capable of establishing an increased stroke per stitch while utilizing a usual embroidery frame drive system.